In the hybrid automatic repeat request (Hybrid Automatic Repeat Request, HARQ) technology, a data receiver needs to feed back acknowledgement/negative-acknowledgement (Acknowledgement/Negative-acknowledgement, ACK/NACK) information to a data sender to help to determine whether data is correctly received. In an uplink direction of a 3rd Generation Partnership Project (3rd Generation Partnership Project, 3GPP) Evolved Universal Terrestrial Radio Access (Evolved Universal Terrestrial Radio Access, E-UTRA) system, a user equipment feeds back ACK/NACK information about downlink data reception to a base station through a physical uplink control channel (Physical Uplink Control Channel, PUCCH). The 3GPP E-UTRA system is also known as a Long Term Evolution (Long Term Evolution, LTE) system. In the following description, the PUCCH channel used by the user equipment to feed back ACK/NACK information about downlink data reception to the base station is referred to as an uplink ACK channel.
In the LTE system, the feedback of the ACK/NACK information may be controlled through downlink control information (Downlink Control Information, DCI). The DCI is used to indicate scheduling information transmitted over a PDSCH and is transmitted over a physical downlink control channel (Physical Downlink Control Channel, PDCCH) corresponding to the physical downlink shared channel (Physical Downlink Shared Channel, PDSCH) indicated by the DCI. The DCI includes a transmission power control (Transmission Power Control, TPC) command field, which is used to adjust transmission power of the uplink ACK channel to send the ACK/NACK information. The TPC command field is generally 2 bits long. Particularly, in an LTE time division duplex (Time Division Duplex, TDD) system, one user equipment may feed back ACK/NACK information corresponding to PDSCH data transmission of multiple downlink subframes in one uplink subframe. Specifically, the LTE TDD system supports two ACK/NACK information feedback modes, which are an ACK/NACK multiplexing mode (ACK/NACK Multiplexing Mode) and an ACK/NACK bundling mode (ACK/NACK Bundling Mode) respectively. In the ACK/NACK multiplexing mode, uplink ACK/NACK information corresponding to each PDSCH data transmission is fed back to the base station independently. In the ACK/NACK bundling mode, uplink ACK/NACK information corresponding to multiple times of PDSCH data transmission is fed back to the base station together after a logic AND operation. To support the ACK/NACK bundling mode, a 2-bit downlink assignment index (Downlink Assignment Index, DAI) command field is introduced in the DCI and is used to indicate the number of PDCCHs that carry the DCI.
In an LTE-Advanced (LTE-Advanced, LTE-A) system, a carrier aggregation technology is chosen to support wider bandwidth so as to meet requirements of the International Telecommunication Union (International Telecommunication Union, ITU) on a peak data rate of the 4th generation communications technology. In the carrier aggregation technology, the spectrums of two or more component carriers are aggregated together to get wider transmission bandwidth, and every component carrier has an independent HARQ process. An LTE-A user equipment may be configured with different numbers of uplink and downlink component carriers. When the LTE-A user equipment accesses multiple downlink component carriers simultaneously, ACK/NACK information corresponding to the data transmission over PDSCH of every downlink component carrier is fed back over the uplink ACK channel. When the ACK/NACK information corresponding to the data transmission of multiple downlink component carriers needs to be fed back over a same uplink component carrier, a problem of feeding back the ACK/NACK information corresponding to the data transmission of multiple downlink component carriers over the same uplink component carrier needs to be solved.
With reference to the LTE TDD system, in the LTE-A system, when a user equipment is configured with multiple downlink component carriers to receive data, feedback of the uplink ACK/NACK information corresponding to the data transmission of the multiple downlink component carriers may also adopt the ACK/NACK multiplexing mode or ACK/NACK bundling mode Likewise, the DCI information may be adopted to control the feedback of ACK/NACK information. For example, a TPC command field is used to control the transmission power of an uplink component carrier and a DAI command field is used to support the ACK/NACK bundling mode.
Particularly, in a carrier aggregation LTE-A system, considering the relatively small number of users simultaneously scheduled over multiple downlink component carriers, the uplink ACK channel assignment for the user equipment may be notified by the base station through explicit signaling. One manner is that the base station directly notifies the assigned uplink ACK channel resources through high-level signaling. To increase the statistical multiplexing probability of uplink ACK channels of different user equipment, another manner is that the base station assigns a group of ACK channel resources to the user equipment through high-level signaling and adds an ACK resource indication (ACK Resource Indication, ARI) command field to the DCI information carried by the PDCCH to further indicate which one of the group of high-level assigned uplink ACK channel resources is used currently. The ARI command field does not exist in the LTE system and needs to be introduced additionally in the LTE-A system. The number of bits depends on the number of the high-level assigned uplink ACK channel resources, and generally 2 bits are considered enough.
In the carrier aggregation LTE-A system, to solve the problem of feeding back ACK/NACK information corresponding to the data transmission of multiple downlink component carriers over the same uplink component carrier, it may be necessary to introduce a DAI command field and/or an ARI command field on the basis of the DCI in the LTE system. Therefore, an ACK/NACK information feedback solution that is backward compatible with the LTE system needs to be provided.